Photodynamic therapy (PDT) is a technology of treating incurable diseases such as cancer and the like or treating diseases such as acne and the like without performing an operation by using a photosensitive material (hereinafter, referred to as “photosensitizer”). PDT has been actively studied from the early 21st century, and currently, is being used in order to increase immunity in cancer diagnosis and therapy, autologous bone marrow transplantation, antibiotics, AIDS therapy, skin graft, or arthritis therapy, and thus the application range thereof has gradually widened.
In particular, as for PDT used in cancer therapy, when a photosensitizer, which is a material sensitive to light, is administered into the body and external light is irradiated, the photosensitizer chemically reacts with fluent oxygen in the external light, to generate singlet oxygen or free radical, and this singlet oxygen or free radical induces apoptosis in various lesions and cancer cells to destruct them.
Currently, porphyrin derivatives, chlorine, bacteriochlorin, phthalocyanine, 5-amino-levulinic acid derivatives, and the like, have been known as the photosensitizer used in PDT. Cyclic tetrapyrrole derivatives as the photosensitizer is characterized by being selectively accumulated in cancer cells and exhibiting fluorescence or phosphorescence due to compound property, and thus may be utilized as a reagent for early diagnosis. In addition, since metalloporphyrin in which metal is bound inside the cyclic tetrapyrrole exhibits several characteristics depending on the kind of metal bound thereto, metalloporphyrin is used as a contrasting agent at the time of magnetic resonance imaging (MRI) and thus is applied during the early diagnosis of tumor cells such as cancer cells. Also, 5-amino-levulinic acid derivatives, which are the most widely known photosensitizers, are simply used and have a small molecular weight, which thus comparatively facilitate skin permeation, and have few side effects and thus are stable. In addition, it has been reported that a metallophthalocyanine-based compound in which metal is bound to an inside of phthalocyanine in which pyrrole groups of cyclic tetrapyrrole are conjugated with benzene rings and connected via aza nitrogen, or an inside of naphthalocyanine in which each benzene ring of phthalocyanine is conjugated with another benzene ring, has higher absorption wavelength and molar absorptivity than a general porpyrin based compound.
PDT can selectively remove only cancer cells while maintaining normal cells; eliminate the risk of general anesthesia; and facilitate the operation even with simple local anesthesia alone.
However, PDT is difficult to apply to bulky tumor cells through which light does not pass. In particular, PDT has disadvantages in that the photosensitizer is slow in view of in vivo metabolism and thus remains for a long time in the body, resulting in phototoxic side effects, and scarcely accumulates in the tumor cells, resulting in decreasing the concentration of the photosensitizer in the tumor cells, failing to efficient therapy effects.
Moreover, the half-life of the photosensitizer is long, which causes patients to inconveniently stay in the lightless environment after the treatment, and the photosensitizer is difficult to accumulate in the tumor cells. In addition, treating compounds accumulate in the body for a long time including the therapy time, which causes various side effects in the body. Furthermore, most photosensitizers used for PDT are hydrophilic products, and do not easily penetrate the skin, and thus therapy needs to be implemented several times over a long period, which causes therapy to be excessively long.
Therefore, new photodynamic therapeutic agents capable of having high accumulation ratio specifically in cancer cells, minimal side effects, superior therapy effects and efficiently utilizing biocompatible polysaccharides are required to be developed.